Device with diamond detector with neutron detection

ABSTRACT

A device for neutron detection, comprising in combination with a radiator a nuclear radiation detector on the basis of a diamond crystal plate with contacts formed at the opposite sides thereof, one of which contacts is made blocking in relation to charge carriers and is provided with said radiator, while the opposite contact is made of a material capable, in conjunction with a diamond, of injecting charge carriers under the influence of an applied electric field.

United States Patent U [111 3,723,726

Kozlov i 1 Mar. 27, 1973 [54] DEVICE WITH DIAMOND DETECTOR [56]References Cited WITH NEUTRON DETECTION UNTED STATES PATENTS [75]inventor: U g Kozlov 2,760,078 8/1956 Youmans ....250/83,l x 2,951,9429/1960 Kramish ..250/83.l [73] Assignee: Fizichesky Institut Imeni P N,3,201,590 8/1965 Sun ..250/83.l X

Lebedeva Akatlemii Nauk SSSR, Moscow, USSR. Primary ExaminerArchie R.Borchelt Filed; Oct. 6 Attorney-Waters, Roditi & Schwartz [21] Appl.No.: 863,614 [57] ABSTRACT A device for neutron detection, comprising incom- [30] Foreign Application Priority Data bination with a radiator anuclear radiation detector on the basis of a diamond crystal plate withcontacts Oct. 3, 1969 U.S.S.R. ..1274211 formed at the opposite Sidesthereof one of which 521 U.S. Cl. ..250/83.1, 250/833 R f is madeblocking damn charge 51 Int. Cl .001: 3/00 and is Pmvided with Saidradiator, While the P- [58] Field of Search ..250/83.1, 83.3 R; 11/11Posite Contact is made of a material Capable in junction with a diamond,of injecting charge carriers under the influence of an applied electricfield.

3 Claims, 2 Drawing Figures I 4 i 74 FECOED/A/ "MIA A/ s DEVICE WITHDIAMOND DETECTOR WITH NEUTRON DETECTION The present invention relates todevices for detection of neutrons, for instance, with the aim of neutronspectrometry or neutron flux measurement.

Widely known are devices for neutron detection, comprisingneutron-sensitive means for converting neutrons into ionizing radiation,termed neutron converters or radiators, and nuclear radiation detectorson the basis of silicon, or germanium, or silicon carbide. The radiatoris mounted in front of a detector which detects charged particles,resulting from nuclear reactions induced by neutrons in the radiatormedium.

A limitation of devices with silicon detectors is that when detectinghigh-energy neutrons large background occurs as a result ofneutron-induced reactions with silicon nuclei within a detector.Furthermore, these detectors cannot be used at high temperatures.Germanium detectors should be cooled during operation, although theygive lower background due to neutroninduced reactions than silicondetectors. Silicon carbide detectors can operate at elevatedtemperatures, but they have poor energy resolution and low signal tonoise ratio. In addition, all the detectors described above aresensitive to gamma-radiation background which usually accompaniesneutron irradiation. These detectors have a high noise level at roomtemperature. In some cases the detector does not allow low-energyneutrons to be detected for their spectrometry. Finally, radiationdamage by neutrons limits the service life of these detectors.

It is an object of the present invention to provide a device for neutrondetection, that will be insensitive to gamma-radiation, give lowbackground due to neutroninduced reactions and can detect neutrons withhigh sensitivity at room and higher temperatures.

In the accomplishment of the above and other objects of the invention,in a device for neutron detection, comprising a radiator convertingneutrons into ionizing radiations, at least one nuclear radiationdetector with an amplifier and means for recording output signals and adetector power supply, according to the invention, in combination with aradiator a nuclear radiation detector is used which is essentially adiamond crystal plate with contacts formed at the opposite sides thereofand designed for applying an electric field to said plate, the platehaving the thickness of the operating range between said contacts notexceeding the distance travelled by charge carriers in the diamondcrystal under the influence of an applied electric field, the contactdisposed on the plate side adapted to be irradiated with ionizingradiation resulting from nuclear reactions induced by neutrons in theradiator medium during neutron detection being made blocking in relationto charge carriers and connected to the input of an amplifier withrecording means, while the contact disposed on the opposite side of theplate is made of a material capable, in conjunction with a diamond, ofinjecting charge carriers under the influence of an applied electricfield and connected through a resistor to a power supply.

With the use of the diamond detector having a blocking contact and aninjecting contact, a radiator may be made as a film of aneutron-sensitive material capable of converting neutrons into ionizingradiations,such film being mounted in front of and close to the blockingcontact of the diamond detector.

For increasing neutron detection efficiency it is advantageous to formthe blocking contact integral with the radiator. In this case theblocking contact of the diamond detector may be formed by a surfacelayer of as carbide of neutron-sensitive material or by a surface layerof the diamond crystal plate, said layer being doped withneutron-sensitive material. This results in converting neutrons intoionizing radiation directly in the blocking contact.

In a device designed for neutron spectrometry, two diamond detectors maybe used. A radiator is disposed between their blocking contacts facingeach other, these contacts being connected to the same amplifying andrecording means summing detector output signals.

For a better understanding of the invention, presented hereinbelow is adescription of an exemplary embodiment thereof 'with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic cross section through a device for neutrondetection with a detector comprised of a diamond crystal plate having ablocking contact and an injecting contact;

FIG. 2 is a sectional side view which shows a device for neutrondetection with two detectors.

A nuclear radiation detector 1 (FIG. 1) is mounted in a metallic housing2 made of a weakly absorbing neutron material, such as aluminum. In somecases the housing may be non-metallic and made, for instance, of glass.The detector 1 is essentially a diamond crystal plate 3 on whoseopposite sides contacts 4 and 5 are provided. The contact 4 is madeblocking in relation to charge carriers and manufactured, for example,from a platinum film. The contact 5 is made of a material capable, inconjunction with a diamond, of injecting charge carriers under theinfluence of an applied electric field and is formed, for example, by asilver film. The thickness d of the operating range of said plate 3disposed between the contacts 4 and 5 does not exceed the distancetravelled by charge carriers in the diamond crystal under the influenceof an applied electric field and is given by where 1 is the mobility ofcharge carriers (electrons or holes), 1' is the lifetime of chargecarriers, E is the applied field strength, 8 is the distance travelledby charge carriers under the influence of the applied electric field.

A radiator 6 of neutron-sensitive material is mounted in front of andclose to the blocking contact 4. Different materials are used for theradiator, depending on the energy of neutrons to be detected, Forexample, for thermal neutron detection radiators containing B or Li areused and the B(N,d)Li" or the Li(N,d)H reactions are utilized. Ifneutron-induced fission is used, a radiator is provided, containing, forinstance, U U Pu for slow neutron detection and U Np Pa Th for fastneutron detection. Fast neutrons may also be detected by scattering ofneutrons in the radiator of hydrogenous material, such as polyethylene,paraffin or metal hydrides. For minimizing the background flux ofthermal neutrons the housing 2 is surrounded by a shield (not shown inthe drawing), made, for instance," of Cd, B or Li For moderating fastneutrons the housing is shielded with B, Li or hydrogenous material suchas paraffin, while this shield is sometimes surrounded by another shieldproduced, for instance, from Cd or B for eliminating the background dueto thermal neutrons.

The diamond detector is connected with the neutron-sensitive radiator atthe side of its blocking contact by various methods. For instance, apolyethylene film may be simply glued to the blocking contact. Theradiator of Li may be formed by evaporating a film of Li onto theblocking contact in vacuum. Fissile materials are applied to one side ofa plate made, for instance, of aluminum and then this plate is attachedto the blocking contact of the diamond detector in different possibleWays, the deposited side of the plate being adjacent to the blockingcontact. Along with these conventional methods, fissile materials may bedirectly electroplated onto the blocking contact. In some cases theblocking contact itself can serve as a radiator. For this purpose it isformed by a surface layer of a carbide of neutronsensitive material,such as boron carbide enriched in 8 In addition the blocking contact ofthe diamond detector may be formed by doping the surface layer of thediamond crystal plate with neutron-sensitive material, for instance,with boron enriched in B or lithium enriched in Li. After appropriatetreatment this layer can serve as both a blocking contact and a radiatorat the same time.

Sometimes the housing is filled at pressures with gases used as aradiator, such as hydrogen with the impurity of heavy gases, or BF;enriched in B, or He. In the lastcase the reaction He (n,p)I-I isutilized. If a solid radiator is used, the housing, on the contrary, issometimes evacuated.

Said diamond detector 1 with the radiator 6 is fixed on a support 7, forinstance, by means of silver paint (paste) subjected to appropriatetreatment. The support 7 made of an electroconductive material isdisposed on the side of the injecting contact 5. A metal lead 8 iswelded to the housing 2 and used for its grounding. Additionally, thehousing 2 has two metal leads 9 and 10, insulated by suitablemetal-insulator seals. The lead 9 welded to the support 7 is used forapplying a voltage to the diamond detector. The insulated lead 10 isjoined to the blocking contact 4 of the diamond detector by a wire 11welded to it for-transmitting the detector signals. The lead 9 isassociated through a resistor 12 with a power supply 13, while the lead10 is connected to the input of an amplifier 14 with recording means 15.

A device with two diamond detectors (FIG. 2) is designed for neutronspectrometry and neutron flux measurement. Additionally it provides fordetecting neutrons within the angle of 4'. This device comprises twonuclear radiation diamond detectors I, mounted in the housing 2. Thedetectors are essentially diamond crystal plates 3 having blockingcontacts 4 and injecting contacts 5. The blocking contact 4 of one orboth detectors is provided with a radiator 6 made of a neutron-sensitivematerial. The detectors are arranged so that their blocking contacts,with the radiator 6 disposed between them, are in intimate contact. Ametallic holder 7 is inserted in the housing. The holder has a lead 8welded to it and two insulated leads 9 and 10. The mounting of thediamond detectors and the insulation of their injecting contacts 5 isaccomplished by means of two insulating gaskets 11 and a nut 12 screwedup into the housing. There are holes in one of the gaskets for thepassage of wires coupling the insulated lead 10 to said blockingcontacts 4 and the lead 9 to said injecting contacts 5. The ionizingradiation resulting from neutron-induced reactions inside the radiatormedium such as Li F (tritons and alpha particles) penetrate both diamonddetectors. The coincident detector pulses are amplified and summed byappropriate apparatus. The amplitude of the total signal and the energyrelease of the reaction being known, one can determine the energy ofincident neutrons In some cases the diamond detectors are placed apartand arranged so that their blocking contacts face each other, while I-Iegas is used as a radiator.

The holder 7 is sometimes provided with three insulated leads, one ofwhich is associated with the injecting contacts of the diamonddetectors, while two other leads are connected to the pertinent blockingcontacts. The detector signals are separatly amplified with appropriateapparatus and then fed to a coincidence circuit. This allows backgroundto be minimized.

The device described hereinabove operates in the following manner.Direct voltage is applied to the diamond detector 1 from the powersupply 13. The neutrons to be detected pass through the housing 2,penetrate the radiator 6 and produce ionizing radiations therein as aresult of nuclear reactions. These ionizing radiations penetrate thediamond detector 1 from the side of its blocking contact 4 and causeionization inside the detector. The resulting charge carriers (electronsand holes) move to the contacts 4 and 5 under the influence of theapplied electric field. The electrons travel to the injecting contact 5,if a positive potential is applied to it. The holes travel to theblocking contact 4. On their movement to the contact 5 some electronsare trapped by traps always present in the diamond crystal. As a result,the diamond crystal plate 3 polarizes. The injecting contact 5 isdesigned to remove said polarization. Since deep traps are present inthe diamond, the injection currents from the contact 5 are limited bythe space charge accumulated by these traps. Thus, the injectioncurrents do not induce significant conductivity and, consequently,noise. However, when field and charge equilibrium inside the diamondcrystal plate is disturbed due to polarization created by incidentionizing radiation, the charge carriers (holes) injected by the contact5 restore the initial steady state of the crystal.

Some holes travelling to the contact 4 may also be trapped. In thiscase, however, the trapped holes are in the ionization zone and can beneutralized by the charge carriers of the opposite sign, i.e., byelectrons. In addition, when detecting heavily ionizing nuclearradiation, losses in the electron-hole plasma are reduced, since thefield strength is higher in the vicinity of the blocking contact 4.

The signal removed from the blocking contact 4 of the diamond detector 1is fed to the input of the amplifier l4 and then to the recording means15, such as a pulse-height analyzer.

For ensuring detection of isotropic neutron fluxes two diamond detectorsfor nuclear radiations may be used. Their injecting contacts are incontact, while the blocking contacts are provided with radiators.

With a view to increasing neutron detection efficiency mosaics or stacksmay be composed of said diamond detectors.

For enhancing the efficiency of detection of shortrange ionizingradiations, such as fission fragments, resulting from nuclear reactionsinduced by neutrons in the radiator medium, the blocking contact of saiddiamond detectors is made permeable to said ionizing radiations.

For decreasing the sensitivity to gamma-radiation background theblocking and injecting contacts of said diamond detectors are formedfrom materials having low atomic numbers.

Said diamond detector having the injecting contact and the blockingcontact provided with the radiator may also be encapsulated in epoxyresins, silicone resins or compounds.

The present device for neutron detection has a number of advantages overthe known devices. It may be used for neutron spectrometry and neutronflux measurement in critical assemblies, inside reactors and outsidetheir protection, in neutron generators. It may also be used as aneutron monitor in various investigations. Because of usage of thediamond detector the device possesses good counting and spectrometricproperties and high signal to noise ratio, operates at room and highertemperatures, has low sensitivity to gammaradiation and negligiblebackground due to neutron-induced reactions. Owing to its compactness,it does not distort neutron flux. Since the diamond detector withstandsheating up to high temperatures, the defects caused by neutrons insidethe diamond detector may be annealed from time to time. This increasesradiation resistance of the device and its service life.

I claim:

1. A device with a diamond detector for neutron detection, comprising incombination: a material converting neutrons into ionizing radiation as aresult of nuclear reactions therein; a diamond nuclear radiationdetector comprising a diamond crystal plate having a blocking contactand an injecting contact formed at the opposite sides thereof andadapted for applying an electric field to said plate when detectingneutrons, said blocking contact being on the plate side which isirradiated and comprises a surface layer of a carbide of the neutronconversion material, whereby neutrons are converted into ionizingradiations directly in said blocking contact, and said contact beingmade blocking in relation to charge carriers, said injecting contactdisposed on the opposite side of the plate comprising a materialcapable, in conjunction with said diamond crystal plate, of injectingcharge carriers under the influence of said electric field, said platehaving a thickness between said contacts equal to or less than themaximum drift length of the charge carriers created in the diamondcrystal plate by the ionizing radiation under the influence of saidelectric field corresponding to the maximum drift rate; a detector powersupply connected to said injecting contact; an amplifier having an inputconnected to said blocking contact and means for recording input sinals.

2. A device according 0 claim 1, wherein said blocking contact of thediamond detector comprises a surface layer on the diamond crystal plate,said layer being doped with the neutron conversion material, wherebyneutrons are converted into ionizing radiations directly in the blockingcontact.

3. A device according to claim 1, comprising two diamond detectors, therespective blocking contacts of said two detectors facing each otherwith a neutron conversion material disposed therein and being connectedto the same amplifying and recording means summing the detector outputsignals.

1. A device with a diamond detector for neutron detection, comprising incombination: a material converting neutrons into ionizing radiation as aresult of nuclear reactions therein; a diamond nuclear radiationdetector comprising a diamond crystal plate having a blocking contactand an injecting contact formed at the opposite sides thereof andadapted for applying an electric field to said plate when detectingneutrons, said blocking contact being on the plate side which isirradiated and comprises a surface layer of a carbide of the neutronconversion material, whereby neutrons are converted into ionizingradiations directly in said blocking contact, and said contact beingmade blocking in relation to charge carriers, said injecting contactdisposed on the opposite side of the plate comprising a materialcapable, in conjunction with said diamond crystal plate, of injectingcharge carriers under the influence of said electric field, said platehaving a thickness between said contacts equal to or less than themaximum drift length of the charge carriers created in the diamondcrystal plate by the ionizing radiation under the influence of saidelectric field corresponding to the maximum drift rate; a detector powersupply connected to said injecting contact; an amplifier having an inputconnected to said blocking contact and means for recording inputsignals.
 2. A device according to claim 1, wherein said blocking contactof the diamond detector comprises a surface layer on the diamond crystalplate, said layer being doped with the neutron conversion material,whereby neutrons are converted into ionizing radiations directly in theblocking contact.
 3. A device according to claim 1, comprising twodiamond detectors, the respective blocking contacts of said twodetectors facing each other with a neutron conversion material disposedtherein and being connected to the same amplifying and recording meanssumming the detector output signals.